Various methods are used to form a hard coating (also referred to as a protective layer) having excellent abrasion resistance and chemical resistance on various molded products, such as resin products or wooden products. For example, a sheet on which a coating layer is formed of a photo-curable resin composition on a release layer of a base having release properties (such sheets are referred to as a “transfer material”) may be used. In this case, the coating layer is attached to the surface of a molded product, and the base is separated, thereby forming a hard coating. Another method of forming a hard coating uses a sheet in which a coating layer is formed on one side of a base having no release properties and an adhesive layer is formed on the opposite side of the base as needed (such a sheet is referred to as a “surface protective sheet”). In this method, the base of the surface protective sheet is attached to the surface of a molded product to form a hard coating.
The transfer material or surface protective sheet may include a decorative layer, such as a patterned layer or deposition layer, in a proper position as necessary. The transfer material mostly includes a patterned layer or deposition layer formed between the base and the coating layer, and the surface protective sheet generally includes a patterned layer or deposition layer formed on an opposite side of the base to the coating layer.
When forming a hard coating using a transfer material or a surface protective sheet, a pre-curing process is carried out, in which light is irradiated prior to application of the transfer material or surface protective sheet to a molded product to photo-cure a coating layer. However, in this case, a cured hard coating can be separated from a curved potion or cracks can occur on the hard coating upon application of the transfer material or surface protective sheet to the molded product.
Thus, in application to a molded product, an un-cured coating layer is bonded to the surface of the molded product and then cured, which is referred to as a post-curing (or after-curing) method. However, the post-curing process has the following problems.
A transfer material or surface protective sheet is generally prepared using a machine, such as a gravure rotary printing machine. However, when the post-curing process is used to form, for example, a patterned layer, a deposition layer, or an adhesive layer on a coating layer in formation of a transfer material or to roll a sheet in formation of a surface protective sheet, components of an uncured coating layer may be transferred to a guide roll or components used for forming the patterned layer, or adhesive layer may be transferred to the coating layer. Further, components of the coating layer may be transferred back to the guide roll for forming the patterned layer or adhesive layer (a so-called back trapping phenomenon).
Accordingly, when the post-curing process is used, special equipment or an additional process including a drying process is involved in forming a coating layer in order to remove fluidity or tack of the coating layer before photo-curing. However, in this case, the coating layer, the patterned layer, or the adhesive layer may not be formed at the same time and substantial costs for designing separate equipment are needed, thereby reducing productivity of a transfer material or surface protective sheet and considerably increasing manufacturing costs.